To achieve energy efficiency, a common goal in building construction, it is necessary to insulate and minimize air infiltration through ceilings. Typical ceiling construction to minimize air infiltration includes installing insulation between the rafters and installing a vapor barrier, such as polyethylene, under the rafters, and applying an interior covering such as sheetrock over the vapor barrier.
Unfortunately, the installation of conventional electrical boxes to ceilings oftentimes compromises the air tightness of a building. Typically, electrical boxes are fastened to the rafters and wiring pulled into the boxes prior to installation of the vapor barrier. The vapor barrier and sheet rock are typically installed over the electrical boxes and holes then cut in the vapor barrier and sheetrock to expose the electrical boxes.
A couple of problems arise when holes are cut in the vapor barrier for conventional electrical boxes. Since the front edge of the electrical box extends to approximately level with the interior ceiling, the hole is typically cut larger than the periphery of the electrical box. With the hole larger than the electrical box, air seepage can occur around the periphery of the electrical box. The air seepage occurs as a result of the disruption of the integrity of the vapor barrier around the box and the inability of the conventional electrical box to create a proper seal with the vapor barrier.
A second source of air infiltration is through the conventional electrical box itself. This can occur as a result of oversized knockouts in the box and the lack of proper sealing materials around the electrical cables leading into the box.
What is needed therefore is an electrical fixture mounting assembly that stops air infiltration around the periphery of the box and also enables proper sealing at the knockout areas wherein the electrical cables enter the box.